Certain construction vehicles, such as backhoes, end loaders, pans and other earthmovers, have maximum payloads which are a substantial part of the gross weight of the vehicle. These vehicles are often driven with a full payload and subsequently with no payload, causing the operator to experience a sharp difference in driving characteristics. For example, in a routine end loader operation, the operator acquires a bucketful of earth and then carries it to a second location. At the second location, the operator dumps the bucket and then in an empty condition returns to the first location to dig more earth.
One of the vehicle handling problems caused by the weight variation relates to putting the vehicle in gear to go from one location to the other. The transmission in such vehicles is more or less gradually engaged by use of a clutch. The transmission control valve controls application of hydraulic fluid pressure to the transmission clutch. On the one hand, engagement of the transmission under empty-load conditions should not be too jerky or abrupt, or degradation of operator control of the vehicle could result. On the other hand, actuation of the clutch under full-load conditions should not be so gradual that the controls feel sluggish. Acceptable handling characteristics under these two conditions are often difficult if not impossible to obtain by use of conventional transmissions and clutches. A need therefore persists for transmission/clutch arrangements which are not too jerky under empty load and are acceptably responsive under full load.